Asphalt offers outstanding binding and waterproofing characteristics. These physical attributes of asphalt have led to its widespread utilization in paving, roofing, and waterproofing applications. For instance, asphalt is used in manufacturing roofing shingles because it has the ability to bind sand, aggregate, and fillers to the roofing shingle while simultaneously providing excellent water barrier characteristics.
Naturally occurring asphalts have been used in various applications for hundreds of years. However, today virtually all of the asphalt used in industrial applications is recovered from the refining of petroleum. Asphalt, or asphalt flux, is essentially the residue that remains after gasoline, kerosene, diesel fuel, jet fuel, and other hydrocarbon fractions have been removed during the refining of crude oil. In other words, asphalt flux is the last cut from the crude oil refining process.
To meet performance standards and product specifications, asphalt flux that is recovered from refining operations is normally treated or processed to attain desired physical characteristics and to attain uniformity. For instance, asphalt that is employed in manufacturing roofing products typically needs to be treated to meet the special requirements demanded in roofing applications. More specifically, in the roofing industry it is important to prevent asphaltic materials from flowing under conditions of high temperature, such as those encountered during hot summers. In other words, the asphaltic materials used in roofing products should maintain a certain level of stiffness (hardness) at high temperatures. This increased level of stiffness is characterized by a reduced penetration value, an increased viscosity, and an increased softening point.
To attain the desired set of properties needed in many applications, such as in manufacturing roofing tiles, the base asphalt flux is normally air blown to attain the required level of stiffness. During the air blowing procedure the asphalt reacts with oxygen in the air which results in it having a lower penetration value and a higher softening point. Air blowing catalysts are frequently added to the asphalt flux being air blown to reduce the time needed to attain the desired increase in softening point and reduction in penetration value. Various chemicals and/or polymer modifiers are also frequently added to the asphalt (before or after air blowing) to attain the desired combination of properties needed in the particular application in which the asphalt will ultimately be used.
In conventional air blowing methods air is pumped through the asphalt flux for a period of about 2 to about 10 hours while it is maintained at an elevated temperature which is typically within the range of 400° F. (204° C.) to 550° F. (288° C.). The air blowing process optimally results in the stiffness and the softening point of the asphalt flux being significantly increased. This is highly desirable because ASTM D 3462-96 (Standard Specification for Asphalt Shingles Made from Glass Felt and Surfaced with Mineral Granules) requires roofing asphalt to have a softening point which is within the range of 190° F. (88° C.) to 235° F. (113° C.) and for the asphalt to exhibit a penetration at 77° F. (25° C.) of above 15 dmm (1 dmm=0.1 mm). In fact, it is typically desirable for asphalt used in roofing applications to have a penetration which is within the range of 15 dmm to 35 dmm in addition to a softening point which is within the range of 185° F. (85° C.) to 235° F. (113° C.).
In typical air blowing techniques the oxygen containing gas is introduced and distributed into the bottom 14 of an un-agitated blow still 15 through spargers 16. Once the oxygen containing gas (air) is in the system it travels up through the asphalt 17 and ultimately reaches the surface of the asphalt 8 at the top of the blow still as illustrated in FIG. 1. As the air travel through the asphalt from the bottom to the top of the blow still it is available to react with the asphalt flux being oxidized. The rate of chemical reactions occurring within the blow still is known to be limited by the diffusion of oxygen in the air bubbles traveling through the system. It is also known that mechanical agitation has a significant effect on the oxidation processing time by increasing the surface area of the air bubbles in the system. In any case, conventional asphalt oxidation techniques are currently mass transfer limited.
Air blowing has been used to increase the softening point and stiffness of asphalt since the early part of the twentieth century. For example, U.S. Pat. No. 2,179,208 describes a process wherein asphalt is air blown at a temperature of 300° F. (149° C.) to 500° F. (260° C.) in the absence of a catalyst for a period of 1 to 30 hours after which time a polymerization catalyst is added for an additional treatment period of 20 to 300 minutes at a temperature of 225° F. (107° C.) to 450° F. (232° C.).
Over the years a wide variety of chemical agents have been used as air blowing catalysts. For instance, ferric chloride, FeCl.3 (see U.S. Pat. No. 1,782,186), phosphorous pentoxide, P2O5 (see U.S. Pat. No. 2,450,756), aluminum chloride, AlCl3 (see U.S. Pat. No. 2,200,914), boric acid (see U.S. Pat. No. 2,375,117), ferrous chloride, FeCl2, phosphoric acid, H3PO4 (see U.S. Pat. No. 4,338,137), copper sulfate CuSO, zinc chloride ZnCl2, phosphorous sesquesulfide, P4S3, phosphorous pentasulfide, P2S5, and phytic acid, C6H6O6(H2PO3)6 (see U.S. Pat. No. 4,584,023) have all been identified as being useful as air blowing catalysts.
U.S. Pat. No. 2,179,208 discloses a process for manufacturing asphalts which comprises the steps of air-blowing a petroleum residuum in the absence of any added catalysts while maintaining the temperature at about 149° C. to 260° C. (300° F. to 500° F.) and then heating the material at a temperature at least about 149° C. (300° F.) with a small amount of a polymerizing catalyst. Examples of such polymerizing catalysts include chlorosulphonic, phosphoric, fluoroboric, hydrochloric, nitric or sulfuric acids and halides as ferric chloride, aluminum bromide, chloride, iodide, halides similarly of copper, tin, zinc, antimony, arsenic, titanium, etc. hydroxides of sodium, potassium, calcium oxides, sodium carbonate, metallic sodium, nitrogen bases, ozonides and peroxides. Blowing with air can then be continued in the presence of the polymerizing catalyst.
Several patents describe the application of phosphoric mineral acids in modifying asphalt properties. For instance, U.S. Pat. No. 2,450,756 describes a process to make oxidized asphalts by air blowing petroleum hydrocarbon in the presence of a phosphorus catalyst, including phosphorus pentoxide, phosphorus sulfide, and red phosphorus. U.S. Pat. No. 2,762,755 describes a process of air blow asphaltic material in the presence of a small amount of phosphoric acid. U.S. Pat. No. 3,126,329 discloses a method of making blown asphalt through air blowing in the presence of a catalyst which is an anhydrous solution of 50 weight percent to 80 weight percent phosphorus pentoxide in 50 weight percent to 20 weight percent phosphoric acid having the general formula HmRnPO4.
U.S. Pat. No. 2,762,756 discloses a process for manufacturing asphalt which comprises: passing an asphalt charge stock through as ejector into which air is inducted simultaneously by the flow of the said charge stock, whereby said charge stock is dispersed in air, the ratio of said asphalt charge to air being from about 1.6 to about 5.6 gallons per minute per 1 cubic foot of air per minute, and the temperature being maintained between about 300° F. and about 550° F.; and discharging the reaction product of said asphalt charge stock and air directly into the vapor space of a separator.
United States Patent Application Publication No. 2012/0132565 A1 discloses a process for increasing the softening point of asphalt comprising the following steps: providing a liquid jet ejector comprising a motive inlet, a motive nozzle, a suction port, a main ejector body, a venturi throat and diffuser, and a discharge connection; conducting a preheated asphalt feed including fresh asphalt and recycled oxidized asphalt, at a temperature from 125° C. to 300° C., as the motive liquid into the motive inlet of the liquid jet ejector; drawing atmospheric air or compressed air into the suction port of the liquid jet ejector; mixing the preheated asphalt within the main ejector body with the air from the suction port of the liquid jet ejector to form a mixture; conducting the mixture to a heated and pressurized oxidizer vessel; collecting an off-gas from the overhead of said oxidizer vessel and an oxidized asphalt product stream from the bottoms of said oxidizer vessel, wherein said oxidized asphalt product stream has softening temperature greater than the preheated asphalt feed; and recycling a portion of the oxidized asphalt product stream back to the liquid jet ejector to form the recycled oxidized asphalt.
United States Patent Application Publication No. 2014/0262935 A1 discloses a method for oxidizing asphalt which comprises dispersing an oxygen containing gas throughout an asphalt flux in an oxidation zone while the asphalt flux is maintained at a temperature which is within the range of about 400° F. to 550° F., wherein the oxygen containing gas is introduced into the oxidation zone through a recycle loop. The recycle loop pumps asphalt flux from the oxidation zone and reintroduces the asphalt flux into the oxidation zone as oxygen enhanced asphalt flux. The recycle loop will typically include a pump which pulls the asphalt flux from the oxidation zone and which pumps the oxygen enhanced asphalt flux into the oxidation zone, and wherein the oxygen containing gas is injected into the recycle loop at a point before the asphalt flux enters into the pump.
All of the air blowing techniques described in the prior art share the common characteristic of both increasing the softening point and decreasing the penetration value of the asphalt flux treated. In other words, as the asphalt flux is air blown, its softening point increases and its penetration value decreases over the duration of the air blowing procedure. It has been the conventional practice to air blow asphalt flux for a period of time that is sufficient to attain the desired softening point and penetration value. Today there continues to be a need for a process that can be used to more efficiently air blow asphalt flux to the desired penetration value and softening point needed in specific industrial applications. For example, to air blow asphalt flux to both a softening point which is within the range of 185° F. (85° C.) to 250° F. (121° C.) and a penetration value at 77° F. (25° C.) of above 15 dmm.